Vapor generator



Feb. 23, 1954 M FRlSCH 2,669,975

VAPOR GENERATOR Filed April 29, 1949 3 Sheets-Sheet 1 INVENTOR /ZA/PT//v FXD/5CH ATTO R N EY Feb. 23, 1954 Filed April 29, 1949 M. FRISCH VAPOR GENERATOR 5 Sheets-Sheet f:

/i-nn lo V Yr N n A LA D N m lo lNvENToR /VA/er//v FAD/5CH Feb. 23, 1954 M. FRlscl-i 2,669,975

.VAPOR GENERATOR Filed April 29, 1949 3 Sheets-Sheet 5 557/ 32 89 I 70 72 Je 90 @954 47 54 3 5 t] m w e2 5357 o 60 L 79 e9 flf E s 2/:1 78 76 -xfi w Y l'mventor 38 Gtorneg Patented Feb. 23, 1954 VAPOR GENERATOR Martin Frisch, New York, N. Y., assigner to Foster Wheeler Corporation, New York, N. Y., a corporation of New York Application April 29, 1949, Serial No. 90,483

Claims. (Cl. 122-459) This invention relates to vapor generators and more particularly pertains to steam generators and to a method of and means for generating steam.

It has been determined that fouling of the blades of a turbine can be caused by very pure steam from the steam generator, that is, by steam containing a fraction of one part per rnillion total solids as determined by the conductance method. Certain chemical constituents of boiler water, such as silica, the presence of which is not revealed by the conductance test, escapes from the boiler Water into the steam in vapor form and, at high pressure, hydroxides, chlorides, sulphates, etc. are dissolved by the steam. In high pressure boilers particularly, silica is vaporized in the steam drum, entrained in said steam and passed in vapor form from the drum in admixture with the steam, The silica, because it is vaporized, is not removed by drying of the steam and passes to the turbine where it condenses on the turbine blades in the low pressure, low temperature stages thereof causing a marked reduction in the capacity of the turbine. The amount of silica vaporized in the boiler increases With the pressure, the saturation temperature, and the concentration of the boiler Water from which the steam is released, and decreases as the pH increases. It is necessary, therefore, in order to maintain turbine capacity that only tseam from which dissolved or vaporized solutes have been removed be passed to the turbine. Also, it is highly desirable that any scale formations caused by impurities from the feed Water of a steam generator be conned substantially to tubes which are exposed only to relatively W temperature heating gases.

In accordance With the present invention, steam which is substantially free of dissolved or vaporized solutes is passed Afrom a vapor generator While scale formations from impurities in the feed water of the steam generator are conned substantially to those tubes exposed only to.

relatively low temperature heating eases.

The invention has special application to high pressure, high temperature steam generators which are required to operate with feed water of high initial solid concentration, due t0 the necessity of using high percentages of make-up water, However, the invention is capable of ap- Dlcation to steam generators generally.

In accordance with the present invention, pure steam, that is, steam free of dissolved. or Vaporized salutes.v is produced and concentration of dissolved solids in the boiler water of the Steam. generator is'controlled by arranging the heating surface of the generator in two or more separate heat absorbing sections, each of which has its own independent circulation system. The feed water enters a primary high duty heat absorbing section which is continuously blowne-down to a low duty secondary section. The secondary section comprises a plurality of tubular members with extended surface elements thereon which members are disposed in the path of owvof gases from the primary section and is subjected, there fore, to relatively low rates of heat absorption by convection.

A low boiler concentration is maintained in the highly heated furnace tubes of the primary section, while a much higher concentration is main tained in the moderately heated tubular members of the secondary section. The possibility of damage to the tubes in the primary or radiant heat absorbing section which operates at high heat transfer rates is minimized because in these tubes a low concentration is maintained, while in the secondary (convection) section which is subjected to low rates of heat transfer and low temperatures, high concentration can be tolerated. Also, since the concentration in the primary section Where the major portion of the steam is generated is low in accordance with the present invention, the amount of silica or other solute van porized is low. The steam released in the secondary section, which steam is made from the highly concentrated boiler Water, will have a greater solute concentration but the steam gen erated in the secondary section is relatively small compared'to the total boiler output. In accordance with the present invention, the mixture of steam and Water formed in the secondary section is passed through a separator wherein steam is separated from said mixture, the separated steam thereafter being condensed and the condensate delivered to the primary section, while the steam-free Water is returned to the secondary section. In this manner, entrained Water is removed from the mixture of steam and Water generated in the secondary section and the vapor-ized solute in the separated steam is condensed with said steam and thereby eliminated from the final steam product of the vapor generator of the present invention.

In the present invention, sub-coolingr Of the downcomers of the primary section is also prevented by washing the steam generated in the primary section in a portion of the feed Water as the steam is treated in vapor and liquid sepa' rators thereby heating the feed Waterdto saturartion prior to the feed water entering the down? comers and by condensing steam from the secondary section by direct heat exchange relationship with the remaining portion of the feed water.

The particular features and advantages which characterize the invention will be understood from the following description when considered in connection with the accompanying drawings forming a part thereof and in which:

Fig. 1 is a vertical sectional view illustrating more or less diagrammatically, the upper portion of a steam generator embodying the invention;

Fig. 2 is an enlarged vertical sectional view of the upper portion of Fig. l; Y

Fig. 3 is a horizontal sectional View taken on the line 3 3 of Fig. 1;

Fig. 4 is an isometric view of a section of the steam and water drum illustrated in Fig. 1 on a larger scale;

Fig. 5 is a vertical sectional view, partly in elevation, taken on the line 5 5 of Fig. 1; and

Fig. 6 is an enlarged transverse sectional View taken on line 5-5 of Fig. 2.

Like characters of reference refer to the same or similar parts throughout the several views.

Referring to the drawings, Figs. l and 2, the steam generator of the present invention comprises a setting I5 having therein a combustion chamber II with a front wall I2 and a rear wall i3. IThe front Wall I2 is inclined inwardly at the top thereof, as shown in Fig. 1, to form a roof i4 above which a steam and water drum I5 is positioned in substantial vertical alignment with rear Wall I3. The walls of the combustion chamber l I are lined with water wall tubes, the iront Wall I2 being lined with tubes I6 which connect at the upper end thereof with the bottom of drum l5, while the rear wall I 3 is lined with water wall tubes Il also connected at the upper end thereof with the bottom of steam drum I5. Side wall I B is lined with riser tubes I 9 connected at their upper end with a header 20. Header 20, in turn, communicates with drum I5 through tubes 2I. A side wall, not shown, opposite wall -18 would also be lined with water wall tubes which would connect with an upper header similar to header 20 and which would also communicate with drum I5. The riser tubes I6, I'I and I9 would connect at their opposite ends with headers, not shown, which headers would receive water through a downcomer ZIa. Downcomer Ela is in communication with drum I5 through a plurality of other downcomers 23 and receives water. from drum I5 through said other downcomers.

Rear wall I 3 extends upwardly a distance short of the drum I5 and roof I4 thereby providing a gas outlet 24 for the chamber II across which outlet the upper portion of Water wall tubes I'I extend. Gas outlet 24 communicates with a downwardly inclined gas passage 25 which passage connects with a vertically extending passage 2B. At the end thereof opposite that which communicates with passage 25, the passage 26 is in communication with a nue 27. As shown, a superheater comprising an inlet section 28, an intermediate section 29 and an outlet section 30 is disposed in the path of gases flowing through passage 25 from chamber II through gas outlet 24. The inlet section 23 receives steam from an inlet header 3! which inlet header communicates with drum l5 through steam conduits 32. Intermediate section 2S o f the superheater is in communication with inlet portion 28 through a header 33. and with outlet portion 30 through a d header 34. Superheated steam is withdrawn from the superheater through an outlet header 35 which receives the steam from outlet section 30.

A secondary steam generating section 36 comprises a plurality of tubular members 3l having extended surface members thereon and positioned in passage 26 so that gases flowing through said passage pass in heat exchange relationship with said tubular members. The tubular members 31, as shown, extend transversely of passage 26 and are grouped in an upper group or portion 40 and a lower group cr portion 4l. The tubes of each portion are so connected with one another as to form a continuous flow path from the inlet header 33 to the outlet headers 39 of the secondary section. While the secondary section 36 is shown as comprising an upper portion 40 and a lower portion 4I, the secondary section may be so arranged as to provide a single portion. The inlet header'38 receives boiler water blown-down from the primary section through a boiler water feed conduit 42 which is connected at one end thereof to the header and at the oppcsite end thereof to downcomer 2Ia.

Steam generated in the secondary steam generating section 36, which steam has entrained water therein, is passed to steam and Water separating apparatus prior to the passage of said steam to drum I5. As shown more particularly in Figs. 2, 3 and 5, steam and water separating apparatus 43 comprises vertically extending elongated, substantially cylindrically-shaped headers 44 disposed adjacent one another in a horizontally extending row (Figs. 3 and 5) and to each of which is connected a plurality of riser tubes 45. Headers 44 are positioned at substantially the same level as drum I5 so that the water level WL in the drum and the water level WL' in the headers will be the same. Riser tubes 45 are connected at one end of a horizontally extending section 45 thereof with the upper portion oi' headers 44 above the water level WL in the headers, said one end being in communication with the headers at one side thereof so that steam is introduced into said headers tangentially of the inner periphery thereof. The riser tubes 45 are connected at the opposite end thereof with the outlets 39 of secondary section 35. Each of the headers 44 has an outlet conduit 46 connected to the bottom thereof which conduit also communicates with inlet header 33 of secondary section 35. At the top thereof, headers 44 communicate with steam drum I5 through tubes 41. As shown in Fig. 1, the headers 44 are provided with a blow-down pipe 48 at the bottom thereof, which blow-down pipes are connected to a horizontal header 49. Blowing-down of Water through horizontal header 49 is controlled by a valve 5I).

Steam, prior to passing from drum I5 into superheater inlet header 3| through conduits 32, is treated to eliminate moisture entrained therein which moisture carries dissolved chemicals, mechanically suspended fine particles of solid matters. vapor which condenses as solids and compounds dissolved in the steam. Such treat.- ment is preferably accomplished by apparatus illustrated and described in applicants co-pending United States patent application, Serial No. 90,484, led concurrently herewith. As shown in Figs. 2 and 4, this apparatus comprises partitioning means so disposed in drum i5 as to form steam receiving chambers adjacent the in.- ner periphery of thefdrurn.A 'The partitioning means 'comprises' side plates `5I and'52 vspac'zed from the inner periphery ofthe drum at the opposite sides thereof and which extend longitudinally of said drum to points short of the opposite ends thereof in laterally spaced relationship to one another. The plates l and 52 each have an upper portion 53 and 54 respectively which extends inwardly of the drum and is secured to the longitudinally extending bars 55 and 56 respectively, the bars 55 and 56 being secured to the inner periphery of the drum. The partition plates 5I and 52 also have inwardly nclined bottom portions 51 and 58 inclined inwardly from the peripheral surface of the drum and in spaced relationship thereto. which bottom portions are similar to the top portions 53 and 5d. A partition plate 59 of substantially the same length as plates 5l and 52 extends longitudinally of the drum in spaced relationship with the inner periphery thereof at the bottom, the opposite sides of plate 59 adjoining a longitudinal edge of plates 5I and 52.

Steam condensing chambers 60 and 6I are formed adjacent the upper part of plates 53 and 54 and between said plates and the inner periphery of drum i5 at opposite sides of the drum by metal partition members 62 and 63. The partition members 52 are secured at one end thereof to plate 53 below the inclined portion thereof and extend transversely of the drum to the inner periphery thereof and upwardly along said inner periphery to a point adjacent member 55 thereafter to project inwardly to be secured to the member 55. The partition member 63 is similar to the partition member 62 and is secured at one end thereof to partition 54 and at the cpposite end to member 56. In this manner, steam condensing chambers 60 and 6I are formed, which chambers extend longitudinally of the drum adjacent opposite sides thereof so that the chambers 6i! and 6I receive separated steam from headers llt through tubes lil. These condensing chambers are open at the opposite ends thereof so that they communicate with the interior of the drum but are in fluid-tight relationship with steam receiving chambers 64 and 65, which are directly below condensing chambers 60 and 6i respectively. Steam receiving chambers B4 and 65 extend longitudinally of the drum at opposite sides thereof between partitions 5l and 52 respectively and the inner periphery of the drum respectively. Chambers 64 and 55 are in communication with passage 66 beneath bottom plate 59 and are closed at the opposite ends thereof by end plates 5l and 58 respectively and the passage 6E is closed at the opposite ends thereof by end plates 69 so that steam received within said chambers and passage from the primary section will pass into a central chamber 'I0 of the drum only through steam treating dryers 'H and 12. Central chamber 'l0 extends longitudinally of drum i5 in the central portion thereof, and is donned along the opposite longitudinal sides thereof by a row of steam and water separating boxes lt and a row of steam and water separating boxes 'is respectively. The bottom of chamber "lil, which is defined by partition plate 59, is in communication with downcomers 23 through outlet openings 'i3 in plate 55. Water from chamber 'I5 flows downwardly through openings 'I3 and huid-tight passages 14 which conduct the feed water from chamber 'l0 through passage 66 and out of contact with steam flowing in said passage.

Feed water for the vapor generator of the present invention is fed to drum I5 through a plurality of oi!take conduits 15 and' 15 extending from the opposite sides of a feed water pipe l1 disposed in central chamber 1i) adjacent the bottom thereof and extending longitudinally of the chamber. The olii-take conduits 15 and 16 extend from the opposite sides respectively of pipe 'H and Aare laterally spaced from one another longitudinally of said pipe. Off-takes 'I5 extend transversely of the drum toward bottom portion 5l of partition 5|, through said bottom portion into chamber. 64 thence upwardly along partition 5l and into condensing chamber El), thence along upper portion 53 to a point short of the top of said chamber. Oitakes 16 also extend transversely of the drum I5 toward partition `52 thence through bote tom portion 58 thereof, upwardly along partition 52 into condensing chamber 6I ythereafter to extend along upper portion 54 to a point short of the top of chamber 6|.

The plurality of separating boxes 18 and 'I9 are disposed in laterally abutting relationship with one another in rows which extend longitudinalli7 o partition plates 5i and 52 respectively. As shown in Fig. 4. the separating boxes are substantially square in cross section and have a steam inlet slot at one side thereof adjacent the bottom (Fig. 2), through which steam from chambers 64 and 65 enters the boxes 18 and 19 respectively. Feed water is injected into, boxes 'I8 and 19 tangentially thereof through slots 80 by nozzles 8l and 82 (Fig. 6) which communicate with o-takes I5 and 16 respectively in order to accentuate the whirl Within the boxes 18 and 'I9 and to elect mixing between the feed water and boiler water. The feed water is divided among the plurality of boxes 78 and the plurality of boxes 'l5 so that each box receives an equal share of a predetermined fraction of the total feed water. Boxes it and 15 have steam outlets 83 and 84 respectively at the top thereof through which steam passes into spaces and 86 respectively. The spaces 85 and 86 communicate with the upper portion of chamber 10 through dryers 1I and l2, which, as shown in Fig. 6, are of the chevron type. Each of these dryers (Figs. 4 and 6) comprises a plurality of laterally adjoining longitudinally extending rows each of which has a plurality of vertically extending horizontally spaced Vshaped plates which are positioned in said row with the apex edge of one plate within the area bounded by the next adjacent plate in the row. The separating boxes 'I8 and 19 are open at the bottom thereof and in communication with the lower portion of chamber 10.

Feed water is projected from oil-takes 'l5 and 15 into condensing chambers 60 and- 6l respectively through outlet nozzles 81 and 88; said water impinging on hooked-shaped baille plates 89 and 50. The baffle plates extend longitudinally of chambers 60 and 6I and are so positioned as to direct the feed water downwardly into the chambers. Water from condensing chambers 60 and 6i flows into chamber 10 from the ends of said condensing chambers.

in operation. steam is generated in the primary high duty section of the steam generator of the present invention through the circulation of water from chamber 10 of drum l5 downwardly through openings 13 in partition 59, thence through passage 14 and through the plurality of other downcomers 23 into downcomer Zia. Water from downcomer 2id passes into lower headers, not shown, thence into riser tubes 16,11'A

and I6 in which tubes' steam is generated' by the passage of gases' of combustion in chamber -I lfin indirect heat exchange relationship with said tubes. The mixture of steam and water from these tubes enters steam chambers 64 and 65 through tubes 2 I, which tubes receive steam from headers 20.

Water and steam mixture entering chambers 64 and 65 is centrifuged and a portion of the steam is condensed in the separating boxes 18 and 19 respectively, the mixture entering said boxes through slots 80. Feed water from feed water pipes 11 also iiows into boxes 18 and 19 through pipe 11, passing into boxes 18 through off-takes 15 and nozzles 8| positioned in slots 8G of boxes 18 and into boxes 19 through off-takes 16 and nozzles 82 positioned in slots 8S of boxes 19. The steam and water mixture from chamber 64 together with feed water from nozzles 8l flows into boxes 18 tangentially thereof, while steam and water mixture from chamber 65 likewise passes into boxes 1B thereby centrifuging or whirling the mixture and the feed water. The feed water is heated to saturation by being brought into direct heat exchange relationship with said steam and water mixture and a part of the steam is condensed. Centrifuging or whirling of the steam and water mixture together with the feed water also separates the water, the entrained moisture and any entrained substance of higher specific gravity than the steam from said steam. The separated steam. which is of lighter specific gravity than the feed water and entrained moisture or substance passes upwardly from the center of boxes 18 and 19 through steam outlets 83 and 84 respectively. The separated steam from boxes 18 enters space 85 and is directed by inwardly inclined portion 53 of partition 5| towards dryer 'H through which the steam passes and is dried by flowing through the space between the plurality of plates comprising the dryer. The separated water from boxes 18 flows downwardly along inwardly inclined portion 51 of partition 5I into central chamber of drum l5 while the moisture separated from the steam in dryer 1| also flows downwardly into said chamber. The separated steam from boxes 19 passes upwardly therefrom through outlets 84 and is directed by inclined portion 54 of partition plate 52 into chevron dryer 12, while the separated water flows downwardly from boxes 19 into chamber 18.- Since chambers 64 and 65 are in communication with one another through lower passage 66, the steam from one of said chambers may pass to the other chamber.

By treating the steam and water mixture and the feed water in boxes 18 and 19, as hereinabove described, dry steam only enters chamber 10 thereafter to flow into superheater inlet header 3| through steam conduits 32 and heated water flows into the lower portion of chamber 10 thereafter to pass into other downcomers 23 and thereafter into downcomer 2Ia.

The primary steam generating section is continuously blown-down to the header 33 of secondary steam generating 'section 36v through downcomer `2m, and boiler water feed conduit 42. Water fed from header 38 passes into tubes 31 of upper portion 40 and tubes 31 of lower portion 4| of the secondary section thence into outlet headers 39. Steam is generated in tubes 31 by the passage of gases in indirect heat exchange relationship therewith which gases flow from chamber II-through gas outlet 24 thence v into passage 25 thereafter to enter vlgrtvicallyvl extending passa ge .26. y Y i headers 39 into riser tubes 45 and passes there- Thesteam passes Yfromfoutlet 1 through'into thesteam and water separating headers 44.

In headers 44, steam and water is separated from the mixture thereof owing into the headers from tubes by the whirling or centrifuging of said mixture in the headers. The separated water passes downwardly in headers 44 and enters outlet conduit 4G through which it ilows to inlet header 33 of the secondary section. The secondary section is blown-down through blow-down pipes 48 in headers 44 which blowing-down is controlled by valve 50. The rate of flow of boiler water to the secondary section through boiler water feed conduit 42 will be equal to the evaporation of water in the secondary section 35 plus the blow-down from the secondary section through blow-down pipe 48. Since the headers 44 and the drum l5 are positioned at the same level, the rate of ow of water through conduit 42 to the secondary section will be self-controlling and the water level WL' in the headers 44 will depend on the level WL in steam and water drum I5. When the level in the separator headers 44 drops, due to said evaporation and blow-down, additional water will pass from the main steam drum through downcomers 23, downcomer Zia and feed conduit 42 through the secondary section so that the levels WL and WL will be maintained in equilibrium.

Separated steam from separating headers 44 ows upwardly in the headers to tubes 41 thereafter to ow to condensing chambers and 5l in drum E5. The steam flowing into the condensing chambers is condensed by passing in direct heat exchange relationship with the remaining portion of the feed water flowing from off-takes 15 and 16, into the condensing chambers through nozzles on the end of said off-takes. The feed water from the off-take nozzles is directed downwardly in a sheetr in front of the outlets of tubes 41 by means of baiiles 952. Because of the high heat transfer rates through the direct contact of the feed water sheets and the steam from pipesv 41, the steam will be completely condensed and the vaporized silica or other solute contained in the steam will go back into solution in the condensate. Condensate from chambers and 6l drains downwardly into the feed water in chamber 1B.

Although the invention has been disclosed as applied to the generation of steam, it is not limited thereto but is capable of application to the generation of vapors generally. From the foregoing, it will be perceived that by utilizing the apparatus of the present invention, pure steam that is, steam free of dissolved or vaporized solutes is produced and concentration of dissolved solids in the boiler water of a steam generator is controlled.

It will be understood that changes may be made in the form, location and relative arrangement of the several parts of the apparatus disclosed without departing from the principles of the invention. Accordingly, the invention is not to be limited excepting by the scope of the appended claims.

What is claimed is:

1. A steam generator comprising a setting having a combustion gas outlet, a plurality of steam generating sections in the setting each having a complete circulatory circuit, firing means, the ring means, the steam generating sections and gas outlet being so arranged in relationship to onev another that gases of combustion owing to the outlet pass in heat exchangev relationship with`one of said sections prior to flowing in heat exchange relationship with another section, means for conducting water from said one section to said other section, separating means associated with said other section for receiving all of a mixture of steam and water generated in said other section and comprising a centrifugal separator in which the steam and Water are separated from the mixture thereof by centrifuging, a steam oitake for said steam generator in communication with said one section only, blowdown means connected to a concentrated water containing portion of said other section, and means for condensing all of the steam separated in the centrifugal separator by passing it in heat exchange relationship with at least part of the feed water for the steam generator and adding the resulting condensate to thewater of said one section by conducting it out of contact with the steam generated therein to a water containing portion thereof.

2. The steam generator of claim l wherein the separating means comprises a substantially cylindrically shaped chamber disposed with its longitudinal axis extending in a substantially vertical plane, the chamber being in communication with said other steam generating section so that a mixture of steam and water therefrom is introduced into the chamber tangentially thereof and steam and Water are separated from the mixture thereof by centrifugal force.

3. A steam generator comprising a setting having a combustion gas outlet, a primary steam generating section having a complete circulatory circuit comprising an upper steam and water drum with downcomer and riser tubes in communication therewith, the downcomer tubes communicating with the drum to receive Water therefrom and the riser tubes communicating with the drum to discharge steam thereinto, a secondary steam generating section having steam generating surface at a level lower than said drum and a complete circulatory circuit separate from the primary section, ring means, the ring means, steam generating sections and gas outlet being so arranged in relationship to one another that gases of combustion owing to the outlet pass in heat exchange relationship with the primary section prior to owing in heat exchange relationship with the secondary section, means for conducting Water from the primary section to said f secondary section, a steam offtake for said steam generator in communication with said primary section only, steam and Water separating means comprising a housing having a substantially cylindrically-shaped chamber, the housing being 10 disposed so that the longitudinal axis of the chamber extends in a substantially vertical plane, the chamber being in communication with said other steam generating section to conduct separated water thereto, means for introducing all of a mixture of steam and water from the secondary section into the chamber tangentially thereof above the level of liquid therein thereby separating steam and Water from the mixture thereof by centrifugal force, blowdown means connected to a concentrated water containing portion of said secondary section, and means for condensing all of the steam generated in said secondary section by passing it in heat exchange relation with at least part of the feed water for the steam generator and adding the resulting condensate to the Water of said primary section by conducting it out of contact with the steam generated therein to a water containing portion thereof.

4. The steam generator of claim 3 wherein the secondary section comprises an economizer disposed in convection heat exchange relationship with said gases of combustion, and blow-down means for the steam generator communicates with the separating means so that separated water is blown-down therefrom.

5. The steam generator of claim 3 wherein steam and water treating means is associated with the primary section, said steam treating means being positioned in said drum and constructed and arranged to bring steam and feed water into heat exchange relationship with one another and thereafter separate the steam and water, the steam treating means also communieating with the steam offtake so that separated steam passes from the treating means thereto and with said drum so that separated water ows thereinto.

MARTIN FRISCI-I.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,904,473 Kerr Apr. 18, 1933 1,912,197 Heaton May 30, 1933 1,940,607 Ryan Dec. 19, 1933 2,067,080 Frankel Jan. 5, 1937 2,191,671 Kuhner Feb. 27, 1940 2,289,969 Kerr July 14, 1942 2,290,882 Keenan, Jr. July 28, 1942 2,294,501 Junkins Sept. 1, 1942 2,413,717 Kerr Jan. 7, 1947 2,472,101 Frisch June 7, 1949 

